1. Field of the Invention
The present invention relates to an optical disc reproducing apparatus that reproduces information recorded on an optical disc, and more particularly to an optical disc reproducing apparatus that can reproduce the information from both a digital versatile disc (DVD) and a compact disc (CD). Furthermore, the present invention relates to a semiconductor integrated circuit that is used in such an optical disc reproducing apparatus.
2. Description of the Related Art
Some of the conventional DVD players are of the type that can reproduce the information stored on both DVDs and CDs (i.e., DVD-CD combination player system). Since DVDs and CDs have different data formats, major parts of the circuits for their reproducing systems are independent from one another. A typical circuit structure for the reproducing system of a conventional DVD-CD combination player system is shown in FIG. 9.
Referring to FIG. 9, an optical pickup 2 irradiates laser light onto an optical disc 1 and obtains a reproduced signal from the reflected light. The optical pickup 2 is connected to a digital demodulation/disc determination circuit 3 that converts the reproduced signal into binary data to thereby perform digital demodulation. Also, it determines whether the disc being played is a DVD or a CD based on, for example, the reflected light from the disc.
Reproduced data of a DVD is input to a DVD decoder 20. The DVD decoder has a PI error correction section 21 that performs error correction using inner parity (inner code), and a PO error correction section 22 that performs error correction using outer parity (outer code). For the error correction, a large capacity correction memory 31 is used. A memory block 30 also includes a track buffer memory 32 in addition to the correction memory 31.
Data whose error is corrected and stored in the track buffer memory 32 is transmitted through an AV output section 12 to an MPEG decoder 7 that decodes the data, to thereby provide video data (V) and audio data (A). The video data is input through a video encoder 8 to a D/A converter 9 to provide the video output signals. The audio data is input to a D/A converter 10 to provide the audio output signals.
A large-scale-integrated (LSI) circuit 40 processes data reproduced from a CD. The LSI for CDs includes a CD error correction section 41 that performs error correction using CIRC (Cross Interleaved Reed-Solomon Code). Data whose error is corrected is output through an audio output section 42 included in the LSI for CDs to the D/A converter 10 to provide an analog audio signal.
In this manner, the DVD reproduction system and the CD reproduction system have independent circuit structures, except that the D/A converter 10 for audio signals is shared.
Japanese laid-open patent application HEI 8-180591 describes an audio signal synchronization method that enables continuous reproduction of an audio signal in both a transmission side apparatus and a receiver side apparatus that operate asynchronously. With the audio signal synchronization method, the transmission side apparatus reproduces data at N-fold speed and stores the data in a memory on the receiver side apparatus, and the receiver side apparatus reads out the data at the standard speed.
Japanese laid-open patent application HEI 8-335364 describes an optical disc reproducing device that is capable of reproducing video CDs and preventing dropout due to external vibrations and thereby enhancing resistance to vibration at the time of reproduction of data on musical CDs. In the optical disc reproducing device, an optical disc is rotated faster than the standard speed to accumulate reproduced data in a memory. When a track jump or focus error is detected, a track position before interruption of the data is re-accessed.
Alternatively, Japanese laid-open patent application HEI 10-69728 describes a disc reproducing apparatus that prevents the generation of sound skips due to external impacts without using a large capacity memory. In the disc reproducing apparatus, which is based on the assumption that the response characteristic of the tracking servo improves at a high-speed that is faster than the standard speed, data of n frames is read out from a disc that is rotated at a high speed, and then the pickup is jumped to the inner side by m tracks to read out the next n frames.
However, Japanese laid-open patent application HEI 8-180591 does not describe any countermeasures when reading errors occurs due to external vibrations. Japanese laid-open patent application HEI 8-335364 does not describe any concrete methods to connect together or to associate initially reproduced data and data reproduced after re-access. Furthermore, Japanese laid-open patent application HEI 10-69728 does not describe any countermeasures when reading errors occur in a high-speed reproduction, or methods for connecting data together.
In the case of CD-ROMs or video CDs, borders between sectors can be recognized with synchronizing patterns. However, in the case of audio CDs, only continuous audio data is recorded, so that borders between sectors cannot be recognized. Therefore, in effect, properly connecting data together in an audio CD is not simple. Conventionally, connection of data is performed by detecting whether or not data in specified regions concur with one another. However, substantial errors may be included in a bad disc, which causes problems in that, for example, an algorithm becomes complicated for accurately determining the concurrence of data.
In view of the problems described above, in accordance with a first object of the present invention, in an apparatus that can reproduce information stored on a CD, when subcodes included in a CD format (including an audio CD and a video CD) are reproduced, jitter is compensated for or corrected and the subcodes are synchronized with the data. The term xe2x80x9cjitterxe2x80x9d in the context of the reproducing apparatus refers generally to the degree of error in synchronization between information read from the optical disc (input data) and the reproduced information (output data). It is another object of the present invention to prevent interruptions of sound or pictures by connecting data together using the subcode data. Furthermore, it is another object of the present invention to obtain the above-described effects without increasing the memory capacity in an apparatus that can reproduce both DVDs and CDs. In addition, it is yet a further object of the present invention to provide a semiconductor integrated circuit that is to be used in an optical disc reproducing apparatus such as the one described above.
To solve the problems described above, an optical disc reproducing apparatus in accordance with the present invention includes: an error correction means or unit or circuit that performs error correction processing for signal data reproduced (read) from a CD; a memory or memory means that stores the signal data whose error is corrected; data output means or unit or circuit that reads out the signal data stored in the memory means according to a reference clock; and a subcode detection/jitter correction means or unit or circuit that detects subcode data reproduced from (read from) the CD and outputs the subcode data to the memory in synchronism with outputting of the signal data by the error correction unit, to thereby remove or correct jitter.
Also, in an embodiment of the present invention a semiconductor integrated circuit comprises the error correction means or unit or circuit, the data output means or unit or circuit, and the subcode detection/jitter correction means or unit or circuit as described above.
The optical disc reproducing apparatus or the semiconductor integrated circuit described above may further include a controller or control means that controls rotation of a CD at a high-speed that is faster than a standard speed and stores signal data reproduced therefrom in the memory or memory means, and, when a reproduction tracking fails or an error greater than a specified amount is generated in the signal data in a region of the CD, reproduces (reads) again the signal data in the region of the CD based on subcode data output by the subcode detection/jitter correction means or circuit or unit and stores the same in the memory.
Alternatively, the optical disc reproducing apparatus or the semiconductor integrated circuit described above may further include a controller or control means that controls rotation of a CD at a high-speed that is faster than a standard speed and stores signal data reproduced therefrom in the memory, changes reproduction conditions, and reproduces (reads) again the signal data in the region of the CD based on subcode data output by the subcode detection/jitter correction means or circuit or unit and stores the same in the memory.
The reproduction conditions may include at least one of a servo characteristic in CD rotational speed control, a servo characteristic in position control of an optical pickup, a gain of the optical pick up and a characteristic in wave-form equalization of the reproduced signal.
With the present invention having the features described above, when subcodes included in a CD format or a video CD format are reproduced (read), jitter is removed by synchronizing the subcodes with the signal data. Moreover, interruptions of sound and pictures can be prevented by connecting the data together using the subcode data.
The optical disc reproducing apparatus in accordance with the present invention may be an apparatus that can reproduce the information stored on both DVDs and CDs.
In this case, the optical disc reproducing apparatus or the semiconductor integrated circuit may further include a DVD decoder means or unit or circuit that stores signal data reproduced (read) from the DVD in the memory and decodes the same. Also, the optical disc reproducing apparatus or the semiconductor integrated circuit may further include: DVD access control means or controller that generates addresses for the DVD decoder to control accesses thereof; CD access control means or controller that generates addresses for CD error correction means or unit to thereby control accesses thereof; and upper address generation means or generator that generates upper addresses for accessing the memory based on the address generated by the DVD access control means (controller) or the address generated by the CD access control means.
In this manner, the CD data reproduction capacity can be improved by commonly sharing a memory for the DVD and the CD, without increasing the memory capacity.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.